The present invention relates to dye laser fluid replenishment systems. Dye lasers have been popular in the art for a number of years because of the ability to tune the wavelength of the laser output beam. Dye lasers are also capable of relatively high power output radiation levels. This permits dye lasers to be useful in many applications such as photo induced chemical and medical reactions, photo detection schemes including spectroscopy and pollution detection. One of the features of dye lasers is that the lasing medium is a fluid which is rapidly passed through the region of active lasing insuring quick replenishment between pulses of laser output. In this manner, a high power, high repitition rate beam can be achieved.
As a result of the lasing activation of the fluid dye solution, typically by high power flashlamp excitation, the lasable components, such as the dye molecules in the solution, are degraded with each high energy impulse of the flashlamp. Dye solutions also typically include components intended to quench the triplet state of the dye molecule which interferes with laser action. These quenching components of the dye solution can similarly be degraded by the lasing operation. In typical fluid dye lasers the solution contains a complex dye molecule such as a rhodamine dye along with a quenching component such as a cyclooctatetraen which provides triple excited state quenching. These components or others are typically provided as solutes in a water or organic (e.g. alcohol) base solution.
As a dye laser thus constructed may be intended to operate for protracted periods of time it is essential that a supply of usable dye solution be made continuously available for the laser. At high flow rates necessitated by high laser pulse repetition rates, a great deal of dye solution is passed through the laser head per minute. If this solution is recycled back through the laser, even though with each pulse only a portion of the solute has been degraded, by repeated cycling the dye solution becomes rapidly degraded to the point where laser performance, in terms of power output, can be reduced to unacceptable levels. If on the other hand a supply of fresh lasing fluid is provided in a sufficient volume to accommodate the laser over protracted periods, and the once utilized dye solution is discarded, the cost of operation becomes extremely high.
In one example of a mechanism to avoid this, shown in U.S. Pat. No. 4,364,015, the dye is recycled through the laser on a continuous basis from a reservoir. A small portion of the thus circulating dye solution is removed from the circuit on a continuous basis and processed in order to remove the degradation products while restoring the solute to a desired concentration level. This small extracted portion, as thus revitalized, is returned to the circuit. There thus results a replenishment of the fluid circulating through the laser with a fresh solution. While this will not prevent the flowing solution from degrading substantially, a steady state balance will be achieved in which degradation will not fall beyond a certain point and laser operation can be adjusted accordingly.